Oil -- typically olive oil -- symbolizes the good that comes from celestial love. Celestial love is love of the Lord, the highest and purest love we can have. The good of celestial love is the desire to be good springing from celestial love: Wanting to do the Lord's will because you love Him. That's not a state many reach, even in heaven, but it's a beautiful goal. This representation makes sense based on the idea that the sun -- the source of all natural light and heat, and thus all natural life -- represents the Lord, the source of all spiritual light, heat and life. Burning oil was the most pure fire available in Biblical times, thus the closest representation of the sun people could create.

3339. In the next life those forms of light, and also those forms of warmth, manifest themselves visually. Angels live within the light of heaven and also within the warmth that has been spoken of. From that light they receive intelligence, and from that warmth the affection for good. Indeed the forms of light seen with their external sight have their origin in the Lord's Divine wisdom, and the forms of warmth which are also felt by them have their origin in the Lord's Divine love. To the extent therefore that spirits and angels possess intelligence in truth and affection for good they are closer to the Lord.